A zebrafish embryo goes from a single-cell to an organism with a functioning nervous system within its first 24 hours of existence. By 24 hours post-fertilization, the embryo has mechanosensory-mediated reflex motor behaviors and by 96 hr the fish is a free-swimming larva. The manifestation of these behaviors is due to the establishment of a simple but effective neural network in the spinal cord and hindbrain of the developing fish. This simple nervous system provides the scaffolding for further expansion during maturation of the organism. Elucidating the mechanisms underlying early nervous system formation in the zebrafish could have a huge impact on our understanding of how many neurological disorders arise in man. The properties of the embryonic/larval zebrafish has made it uniquely suited to study the formation of a neural network- it's fertilized externally, transparent during its development and lends itself easily to molecular techniques such as anti-sense treatment and transgenesis. Anatomical studies using dye labeling have yielded information regarding the morphologies of spinal neurons during these early time points, suggesting the presence of some 11-15 neurons per hemi-segment of the cord between 24-96 HPF. In addition, these studies have provided some insight into how the neurons connect to one another to form a network. However, almost nothing is known about how these neurons communicate amongst each other. It is the purpose of this proposal to generate transgenic fish lines that will enable the elucidation of the neurochemical anatomy of the developing spinal cord. Not only will these fish provide information as to the connectivity of the various spinal and supraspinal pathways, but they will also provide markers for use in functional studies utilizing either co-expression (e.g., with calcium indicators) or electrophysiological approaches. In addition, they can provide markers for specific neuronal types that can be used in forward genetic screens aimed at identifying genes required for either phenotype or connectivity decisions in these cells [unreadable] [unreadable]